Earthquake hazard in West Tennessee

This winter will mark the bicentennial anniversary of one of the largest series of earthquakes to occur in the history of North America. These earthquakes occurred close to home, in the New Madrid seismic zone, which spans the lower Mississippi Valley, from just west of Memphis into southern Illinois.

According to the U.S. Geological Survey, it is the nation’s most seismically active area east of the Rocky Mountains, and it continues to be an area of ongoing small and moderate earthquakes.

It was in this location that, in the winter of 1811-1812, a series of at least three major earthquakes occurred. In addition to intense ground shaking, these historical earthquakes caused landslides along the banks of the Mississippi River bluffs, from Mississippi to Kentucky. Survivors reported that cracks opened in the earth’s surface, and the ground rolled in visible waves.

According to the USGS, the scientific community is concerned with the possibility that another major earthquake could occur in the near future within the New Madrid seismic zone.

Some recent media reports have claimed that the New Madrid seismic zone may be shutting down. The argument, based on global positioning system (GPS) data from the past several years, indicates that there is no buildup of stress in the area, and that the region is no longer hazardous.

However, in 2006, a workshop was held by the USGS to determine the status of earthquake hazards in the Eastern U.S. The experts in attendance considered the previously mentioned GPS data, but due to other factors, such as geological record and continuing seismic activity, they determined that there is indeed still a significant risk for major earthquakes in the New Madrid seismic zone.

The USGS and the Center for Earthquake Research and Information of the University of Memphis currently estimate that the chance of a magnitude 7.5-8.0 earthquake occurring, such as the ones of 1811-1812, within the next 50 years is about 7-10 percent. They estimate the likelihood of a magnitude 6.0 or larger earthquake within the next 50 years to be about 25-40 percent.

In 1811, the central Mississippi Valley was sparsely populated. Today, however, it is inhabited by millions of people. There are major metropolitan areas in the region, such as the cities of St. Louis and Memphis. In contrast to seismically active areas, like California, most buildings in this region are not built to withstand earthquakes.

Today, a repeat event of the 1811-1812 earthquakes would be expected to cause the same types of catastrophic ground failures that occurred before, but with much greater loss due to today’s increased population and development.

Depending on the magnitude and location of the earthquake, areas affected could include northeastern Arkansas, southeastern Missouri, western Tennessee and Kentucky, and southern Illinois. In addition to major building damage, roadways could become impassable, bridges could fail, and agriculture could be disrupted. Also, farmland flooding could contaminate rivers and streams with agricultural chemicals.

Unlike other emergency situations, such as severe weather, earthquakes occur without warning. Recognizing the importance of advance preparation, many organizations, local, state, and federal, are joining together to continuously plan actions that will reduce damage if a major earthquake occurs.

The Central United States Earthquake Consortium,is a partnership of the federal government and the eight states, including Tennessee, most affected by earthquakes in the central United States. According to the director of McNairy County Emergency Management, Rudy Moore, CUSEC often works with our local government to coordinate planning and public outreach.

“We’re constantly planning for it to be a catastrophic event,” says Moore. “We have to look at worst case scenario.”

In the event of an earthquake, Moore advises to “drop, cover, and hold.” Individuals should seek cover from falling debris under a desk or other sturdy object.

Moore also stressed the importance of individuals being prepared by having enough provisions, such as water, food, and medical supplies, to last for at least three days. “Anything you can do to help prepare yourself and your family to take care of immediate needs is good,” says Moore.